1. Field of Invention
The present invention relates to a method of manufacturing complementary metal-oxide-semiconductor (CMOS) photosensitive devices. More particularly, the present invention relates to a method of manufacturing the color filter of a CMOS photosensitive device that reduces the number of fabricating steps, and thus saves processing time and production cost.
2. Description of Related Art
CMOS diode devices are commonly used inside conventional PC cameras and digital cameras. In general, a CMOS diode device comprises a photosensitive layer on a wafer substrate, and there are various light-sensitive regions in the photosensitive layer for the purpose of sensing different colors of light. Furthermore, a color filter is formed above the photosensitive layer, and a film is formed to cover the color filter. In general, light of different colors comes from various directions. When the incoming light passes through the color filter, it is filtered into three colors, for example, red, green and blue, and then is absorbed and detected by the corresponding light-sensitive regions of the photosensitive layer.
FIG. 1 is a flow chart showing the manufacturing steps for fabricating a conventional CMOS photosensitive device. First, in step 10, a first passivation layer is formed over a wafer substrate. Next, a photolithographic process 11 is carried out to form a patterned photoresist layer on the first passivation layer. Thereafter, the first passivation layer is etched in operation 12 using the photoresist layer as a mask. Subsequently, a melting, operation 13 is carried out by heating the first passivation layer. Next, step 14 is carried out to form color filters over the first passivation layer. The color filters are used to filter incoming light so that monochromatic light of different colors is produced. After that, step 15 is carried out to form a planar second passivation layer over the color filters. Then, another photolithographic operation 16 is performed, forming another patterned photoresist layer over the second passivation layer. Next, the second passivation layer is etched in operation 17, using the photoresist layer as a mask. Finally, step 18 is carried out in which micro-lenses are formed on top of the second passivation layer, in locations that correspond to the color filters.
FIGS. 2A through 2K are cross-sectional views showing the progression of manufacturing steps in fabricating a CMOS photosensitive device according to a conventional method. First, as shown in FIG. 2A, a wafer substrate 20 is provided, and a patterned first passivation layer 21 is formed over the wafer substrate 20. Next, as shown in FIG. 2B, a first photoresist layer 22 is formed over the first passivation layer 21, and then the first photoresist layer 22 is patterned. Next, as shown in FIG. 2C, using the patterned first photoresist layer 22 as a mask, the first passivation layer 21 is etched to form an opening 23 that exposes a portion of the wafer substrate 20. The opening 23 is used as a connection pad in subsequent step. Next, as shown in FIG. 2D, the first photoresist layer 22 is removed.
Next, as shown in FIG. 2E. a transparent layer 24 having a planar surface is formed over the first passivation layer 21, the wafer substrate 20 and into the opening 23. Subsequently, as shown in FIG. 2F, color filters including a red filter region 25a, a green filter region 25b and a blue filter region 25care formed over the planar transparent layer 24. The color filters are made from a material including acrylic. Next, as shown in FIG. 2G, a second passivation layer 26 having a planar surface is formed over the red filter region 25a, the green filter region 25b, the blue filter region 25c and the transparent layer 24. Next, as shown in FIG. 2H, a second photoresist layer 27 is formed over the second passivation layer 26, and then the second photoresist layer 27 is patterned.
Next, as shown in FIG. 21, using the patterned second photoresist layer 27 as a mask, the second passivation layer 26 and the transparent layer 24 are etched to form an opening 23a that exposes the wafer substrate 20. The opening 23a serves as a connection pad in subsequent steps. Next, as shown in FIG. 2J, the second photoresist layer 27 is removed. Finally, as shown in FIG. 2K, micro-lens 29a, 29b and 29c are formed over the second passivation layer 26. Micro-lens 29a, 29b and 29c are located above the red filter region 25a, the green filter region 25b and the blue filter region 25c, respectively. In this manner, fabrication of a conventional CMOS photosensitive device is complete.
However, the above method of forming a CMOS photosensitive device has a number of defects, including:
1. The manufacturing operation involves lot of steps. In particular, after the color filters 25 are formed over the first passivation layer 24, another photolithographic and etching operation for another passivation layer has to be carried out. Therefore, cycle time and hence the production cost is increased.
2. The pad opening 23 formed early in the process and may lead to pad charge or pad pit problems when the photoresist is reworked.
In light of the foregoing, there is a need to provide an improved method of manufacturing a CMOS photosensitive device.